Aging is a considerable phenomenon particularly for skin where there is an increase in wrinkles, thickness, stiffness, dryness very likely also due to the exposure of the skin to the sun light for prolonged periods of time. The symptoms caused by the exposure to the sun light are defined as photo-aging and are based on changes at the level of epidermis and derma. It has been proved that photo-aging may be slackened by applying on the skin a cream containing substances such as tretinoin, retinol and derivatives thereof, alpha-hydroxy acids (AHAs).
Tretinoin is a liposoluble compound which is unstable in the living body, and is also irritant on the skin, then it could cause some side effects such as dryness, wounds and scrapings when directly applied on the skin. On the contrary, retinol can be used but, being unstable to light, heat, peroxides and oxygen, may cause additional costs for the presence of various stabilizers. Retinoids including retinol (vitamin A) and retinoic acid, isomers, derivatives and analogs thereof are well known to have beneficial effects in many skin disorders and are used in various cosmetic applications. Retinoids are also well-known to be both liable for degradation and to have a number of side-effects. For this reason there have been many attempts to stabilize retinoids both with supportive formulations and derivatization. One example is the compound retinyl retinoate (retin-15-yl ester retinoic acid (CAS No. 15498-86-9)) formed from retinoic acid and retinol with the purpose of proving a less skin irritant product with higher stability in order to find improved cosmetic use for counteracting skin aging. Other ways of stabilizing retinoids or reducing their side-effects are exemplified in European patent specifications 0366713 and 1351919; and in U.S. Pat. No. 4,677,120.
However, it remains desirable to find agents that improve the stability retinyl retinoate and being a source of retinoids will less side-effects in order to be useful for counteracting skin aging, while also being able to exert a combinatory effect useful to counteract or treat other skin disorders, both cosmetically and therapeutically. The present invention is directed to novel retinoid conjugates capable of such effects.